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      50行代码的MVVM，感受闭包的艺术
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    <h2 id="code"><a href="#code" class="headerlink" title="code"></a>code</h2><pre class="line-numbers language-javascript" data-language="javascript"><code class="language-javascript"><span class="token keyword">class</span> <span class="token class-name">Vue</span><span class="token punctuation">&#123;</span>
    <span class="token function">constructor</span><span class="token punctuation">(</span><span class="token parameter">opt</span><span class="token punctuation">)</span><span class="token punctuation">&#123;</span>
        <span class="token keyword">this</span><span class="token punctuation">.</span>opt <span class="token operator">=</span> opt
        <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">observe</span><span class="token punctuation">(</span>opt<span class="token punctuation">.</span>data<span class="token punctuation">)</span>
        <span class="token keyword">let</span> root <span class="token operator">=</span> document<span class="token punctuation">.</span><span class="token function">querySelector</span><span class="token punctuation">(</span>opt<span class="token punctuation">.</span>el<span class="token punctuation">)</span>
        <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">compile</span><span class="token punctuation">(</span>root<span class="token punctuation">)</span>
    <span class="token punctuation">&#125;</span>
    <span class="token comment">// 为响应式对象 data 里的每一个 key 绑定一个观察者对象</span>
    <span class="token function">observe</span><span class="token punctuation">(</span><span class="token parameter">data</span><span class="token punctuation">)</span><span class="token punctuation">&#123;</span> 
        Object<span class="token punctuation">.</span><span class="token function">keys</span><span class="token punctuation">(</span>data<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token parameter">key</span> <span class="token operator">=></span> <span class="token punctuation">&#123;</span>
            <span class="token keyword">let</span> obv <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Observer</span><span class="token punctuation">(</span><span class="token punctuation">)</span> 
            data<span class="token punctuation">[</span><span class="token string">"_"</span><span class="token operator">+</span>key<span class="token punctuation">]</span> <span class="token operator">=</span> data<span class="token punctuation">[</span>key<span class="token punctuation">]</span>
            <span class="token comment">// 通过 getter setter 暴露 for 循环中作用域下的 obv，闭包产生</span>
            Object<span class="token punctuation">.</span><span class="token function">defineProperty</span><span class="token punctuation">(</span>data<span class="token punctuation">,</span> key<span class="token punctuation">,</span> <span class="token punctuation">&#123;</span>
                <span class="token function">get</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">&#123;</span>
                    Observer<span class="token punctuation">.</span>target <span class="token operator">&amp;&amp;</span> obv<span class="token punctuation">.</span><span class="token function">addSubNode</span><span class="token punctuation">(</span>Observer<span class="token punctuation">.</span>target<span class="token punctuation">)</span><span class="token punctuation">;</span>
                    <span class="token keyword">return</span> data<span class="token punctuation">[</span><span class="token string">'_'</span><span class="token operator">+</span>key<span class="token punctuation">]</span>
                <span class="token punctuation">&#125;</span><span class="token punctuation">,</span> 
                <span class="token function">set</span><span class="token punctuation">(</span>newVal<span class="token punctuation">)</span><span class="token punctuation">&#123;</span>
                    obv<span class="token punctuation">.</span><span class="token function">update</span><span class="token punctuation">(</span>newVal<span class="token punctuation">)</span>
                    data<span class="token punctuation">[</span><span class="token string">'_'</span><span class="token operator">+</span>key<span class="token punctuation">]</span> <span class="token operator">=</span> newVal
                <span class="token punctuation">&#125;</span>
            <span class="token punctuation">&#125;</span><span class="token punctuation">)</span>
        <span class="token punctuation">&#125;</span><span class="token punctuation">)</span>
    <span class="token punctuation">&#125;</span>
    <span class="token comment">// 初始化页面，遍历 DOM，收集每一个key变化时，随之调整的位置，以观察者方法存放起来    </span>
    <span class="token function">compile</span><span class="token punctuation">(</span><span class="token parameter">node</span><span class="token punctuation">)</span><span class="token punctuation">&#123;</span>
        <span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">.</span><span class="token function">call</span><span class="token punctuation">(</span>node<span class="token punctuation">.</span>childNodes<span class="token punctuation">,</span> <span class="token parameter">child</span> <span class="token operator">=></span><span class="token punctuation">&#123;</span>
            <span class="token keyword">if</span><span class="token punctuation">(</span><span class="token operator">!</span>child<span class="token punctuation">.</span>firstElementChild <span class="token operator">&amp;&amp;</span> <span class="token regex"><span class="token regex-delimiter">/</span><span class="token regex-source language-regex">\&#123;\&#123;(.*)\&#125;\&#125;</span><span class="token regex-delimiter">/</span></span><span class="token punctuation">.</span><span class="token function">test</span><span class="token punctuation">(</span>child<span class="token punctuation">.</span>innerHTML<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">&#123;</span>
                <span class="token keyword">let</span> key <span class="token operator">=</span> RegExp<span class="token punctuation">.</span>$<span class="token number">1.</span><span class="token function">trim</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
                child<span class="token punctuation">.</span>innerHTML <span class="token operator">=</span> child<span class="token punctuation">.</span>innerHTML<span class="token punctuation">.</span><span class="token function">replace</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">RegExp</span><span class="token punctuation">(</span><span class="token string">'\\&#123;\\&#123;\\s*'</span><span class="token operator">+</span> key <span class="token operator">+</span><span class="token string">'\\s*\\&#125;\\&#125;'</span><span class="token punctuation">,</span> <span class="token string">'gm'</span><span class="token punctuation">)</span><span class="token punctuation">,</span><span class="token keyword">this</span><span class="token punctuation">.</span>opt<span class="token punctuation">.</span>data<span class="token punctuation">[</span>key<span class="token punctuation">]</span><span class="token punctuation">)</span> 
                Observer<span class="token punctuation">.</span>target <span class="token operator">=</span> child
                <span class="token keyword">this</span><span class="token punctuation">.</span>opt<span class="token punctuation">.</span>data<span class="token punctuation">[</span>key<span class="token punctuation">]</span> 
                Observer<span class="token punctuation">.</span>target <span class="token operator">=</span> <span class="token keyword">null</span>
            <span class="token punctuation">&#125;</span>
            <span class="token keyword">else</span> <span class="token keyword">if</span> <span class="token punctuation">(</span>child<span class="token punctuation">.</span>firstElementChild<span class="token punctuation">)</span> 
            <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">compile</span><span class="token punctuation">(</span>child<span class="token punctuation">)</span>
        <span class="token punctuation">&#125;</span><span class="token punctuation">)</span>
    <span class="token punctuation">&#125;</span>    
<span class="token punctuation">&#125;</span>
<span class="token comment">// 常规观察者类</span>
<span class="token keyword">class</span> <span class="token class-name">Observer</span><span class="token punctuation">&#123;</span>
    <span class="token function">constructor</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">&#123;</span>
        <span class="token keyword">this</span><span class="token punctuation">.</span>subNode <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token punctuation">]</span>    
    <span class="token punctuation">&#125;</span>
    <span class="token function">addSubNode</span><span class="token punctuation">(</span><span class="token parameter">node</span><span class="token punctuation">)</span><span class="token punctuation">&#123;</span>
        <span class="token keyword">this</span><span class="token punctuation">.</span>subNode<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span>node<span class="token punctuation">)</span>
    <span class="token punctuation">&#125;</span>
    <span class="token function">update</span><span class="token punctuation">(</span><span class="token parameter">newVal</span><span class="token punctuation">)</span><span class="token punctuation">&#123;</span>
        <span class="token keyword">this</span><span class="token punctuation">.</span>subNode<span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token parameter">node</span><span class="token operator">=></span><span class="token punctuation">&#123;</span>
            node<span class="token punctuation">.</span>innerHTML <span class="token operator">=</span> newVal
        <span class="token punctuation">&#125;</span><span class="token punctuation">)</span>
    <span class="token punctuation">&#125;</span>
<span class="token punctuation">&#125;</span>
<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<h2 id="重点分析"><a href="#重点分析" class="headerlink" title="重点分析"></a>重点分析</h2><p>接下来梳理一下这段代码的思路，顺便了解一下 MVVM 闭包的艺术：</p>
<ul>
<li>[observe 函数]：首先我们会对需要响应式的 <code>data</code> 对象进行 for 循环遍历，为 <code>data</code> 的每一个 <code>key</code> 映射一个观察者对象<ul>
<li>在 ES6 中，for 循环每次执行，都可以形成闭包，因此这个观察者对象就存放在闭包中</li>
<li>闭包形成的本质是 <strong>内层作用域中堆地址暴露</strong>，这里我们巧妙的用 getter/setter 函数暴露了 for 循环里的观察者</li>
</ul>
</li>
<li>[compile 函数]：我们从根节点向下遍历 DOM，遇到 mustache 形式的文本，则映射成 data.key 对应的值，同时记录到观察者中<ul>
<li>当遍历到  形式的文本，我们正则匹配出其中的变量，将它替换成 data 中的值</li>
<li>为了满足后续响应式的更新，将该节点存储在 key 对应的观察者对象中，我们用 getter 函数巧妙的操作了闭包</li>
</ul>
</li>
<li>在页面初次渲染之后，后续的 <code>eventLoop</code> 中，如果修改了 <code>key</code> 的值，实际会通过 setter 触发观察者的 update 函数，完成响应式更新</li>
</ul>
<h2 id="code-1"><a href="#code-1" class="headerlink" title="code"></a>code</h2><pre class="line-numbers language-javascript" data-language="javascript"><code class="language-javascript"><span class="token operator">&lt;</span><span class="token operator">!</span><span class="token constant">DOCTYPE</span> html<span class="token operator">></span>
<span class="token operator">&lt;</span>html lang<span class="token operator">=</span><span class="token string">"en"</span><span class="token operator">></span>
<span class="token operator">&lt;</span>head<span class="token operator">></span>
  <span class="token operator">&lt;</span>meta charset<span class="token operator">=</span><span class="token string">"UTF-8"</span><span class="token operator">></span>
  <span class="token operator">&lt;</span>meta name<span class="token operator">=</span><span class="token string">"viewport"</span> content<span class="token operator">=</span><span class="token string">"width=device-width, initial-scale=1.0"</span><span class="token operator">></span>
<span class="token operator">&lt;</span><span class="token operator">/</span>head<span class="token operator">></span>
<span class="token operator">&lt;</span>body<span class="token operator">></span>
    <span class="token operator">&lt;</span>div id<span class="token operator">=</span><span class="token string">'app'</span><span class="token operator">></span>
        <span class="token operator">&lt;</span>h3<span class="token operator">></span>姓名<span class="token operator">&lt;</span><span class="token operator">/</span>h3<span class="token operator">></span>
        <span class="token operator">&lt;</span>p<span class="token operator">></span><span class="token punctuation">&#123;</span><span class="token punctuation">&#123;</span>name<span class="token punctuation">&#125;</span><span class="token punctuation">&#125;</span><span class="token operator">&lt;</span><span class="token operator">/</span>p<span class="token operator">></span>
        <span class="token operator">&lt;</span>h3<span class="token operator">></span>年龄<span class="token operator">&lt;</span><span class="token operator">/</span>h3<span class="token operator">></span>
        <span class="token operator">&lt;</span>p<span class="token operator">></span><span class="token punctuation">&#123;</span><span class="token punctuation">&#123;</span>age<span class="token punctuation">&#125;</span><span class="token punctuation">&#125;</span><span class="token operator">&lt;</span><span class="token operator">/</span>p<span class="token operator">></span>
    <span class="token operator">&lt;</span><span class="token operator">/</span>div<span class="token operator">></span>
<span class="token operator">&lt;</span><span class="token operator">/</span>body<span class="token operator">></span>
<span class="token operator">&lt;</span><span class="token operator">/</span>html<span class="token operator">></span>
<span class="token operator">&lt;</span>script<span class="token operator">></span>
document<span class="token punctuation">.</span><span class="token function">addEventListener</span><span class="token punctuation">(</span><span class="token string">'DOMContentLoaded'</span><span class="token punctuation">,</span> <span class="token keyword">function</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">&#123;</span>
    <span class="token keyword">let</span> opt <span class="token operator">=</span> <span class="token punctuation">&#123;</span>el<span class="token operator">:</span><span class="token string">'#app'</span><span class="token punctuation">,</span> data<span class="token operator">:</span><span class="token punctuation">&#123;</span>name<span class="token operator">:</span><span class="token string">'检索中...'</span><span class="token punctuation">,</span> age<span class="token operator">:</span><span class="token number">30</span><span class="token punctuation">&#125;</span><span class="token punctuation">&#125;</span>
    <span class="token keyword">let</span> vm <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Vue</span><span class="token punctuation">(</span>opt<span class="token punctuation">)</span>
    <span class="token function">setTimeout</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">=></span> <span class="token punctuation">&#123;</span>
        opt<span class="token punctuation">.</span>data<span class="token punctuation">.</span>name <span class="token operator">=</span> <span class="token string">'王永峰'</span>
    <span class="token punctuation">&#125;</span><span class="token punctuation">,</span> <span class="token number">2000</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">&#125;</span><span class="token punctuation">,</span> <span class="token boolean">false</span><span class="token punctuation">)</span>
<span class="token keyword">class</span> <span class="token class-name">Vue</span><span class="token punctuation">&#123;</span>
    <span class="token function">constructor</span><span class="token punctuation">(</span><span class="token parameter">opt</span><span class="token punctuation">)</span><span class="token punctuation">&#123;</span>
        <span class="token keyword">this</span><span class="token punctuation">.</span>opt <span class="token operator">=</span> opt
        <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">observe</span><span class="token punctuation">(</span>opt<span class="token punctuation">.</span>data<span class="token punctuation">)</span>
        <span class="token keyword">let</span> root <span class="token operator">=</span> document<span class="token punctuation">.</span><span class="token function">querySelector</span><span class="token punctuation">(</span>opt<span class="token punctuation">.</span>el<span class="token punctuation">)</span>
        <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">compile</span><span class="token punctuation">(</span>root<span class="token punctuation">)</span>
    <span class="token punctuation">&#125;</span>
    <span class="token comment">// 为响应式对象 data 里的每一个 key 绑定一个观察者对象</span>
    <span class="token function">observe</span><span class="token punctuation">(</span><span class="token parameter">data</span><span class="token punctuation">)</span><span class="token punctuation">&#123;</span> 
        Object<span class="token punctuation">.</span><span class="token function">keys</span><span class="token punctuation">(</span>data<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token parameter">key</span> <span class="token operator">=></span> <span class="token punctuation">&#123;</span>
            <span class="token keyword">let</span> obv <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Observer</span><span class="token punctuation">(</span><span class="token punctuation">)</span> 
            data<span class="token punctuation">[</span><span class="token string">"_"</span><span class="token operator">+</span>key<span class="token punctuation">]</span> <span class="token operator">=</span> data<span class="token punctuation">[</span>key<span class="token punctuation">]</span>
            <span class="token comment">// 通过 getter setter 暴露 for 循环中作用域下的 obv，闭包产生</span>
            Object<span class="token punctuation">.</span><span class="token function">defineProperty</span><span class="token punctuation">(</span>data<span class="token punctuation">,</span> key<span class="token punctuation">,</span> <span class="token punctuation">&#123;</span>
                <span class="token function">get</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">&#123;</span>
                    Observer<span class="token punctuation">.</span>target <span class="token operator">&amp;&amp;</span> obv<span class="token punctuation">.</span><span class="token function">addSubNode</span><span class="token punctuation">(</span>Observer<span class="token punctuation">.</span>target<span class="token punctuation">)</span><span class="token punctuation">;</span>
                    <span class="token keyword">return</span> data<span class="token punctuation">[</span><span class="token string">'_'</span><span class="token operator">+</span>key<span class="token punctuation">]</span>
                <span class="token punctuation">&#125;</span><span class="token punctuation">,</span> 
                <span class="token function">set</span><span class="token punctuation">(</span>newVal<span class="token punctuation">)</span><span class="token punctuation">&#123;</span>
                    obv<span class="token punctuation">.</span><span class="token function">update</span><span class="token punctuation">(</span>newVal<span class="token punctuation">)</span>
                    data<span class="token punctuation">[</span><span class="token string">'_'</span><span class="token operator">+</span>key<span class="token punctuation">]</span> <span class="token operator">=</span> newVal
                <span class="token punctuation">&#125;</span>
            <span class="token punctuation">&#125;</span><span class="token punctuation">)</span>
        <span class="token punctuation">&#125;</span><span class="token punctuation">)</span>
    <span class="token punctuation">&#125;</span>
    <span class="token comment">// 初始化页面，遍历 DOM，收集每一个key变化时，随之调整的位置，以观察者方法存放起来    </span>
    <span class="token function">compile</span><span class="token punctuation">(</span><span class="token parameter">node</span><span class="token punctuation">)</span><span class="token punctuation">&#123;</span>
        <span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">.</span><span class="token function">call</span><span class="token punctuation">(</span>node<span class="token punctuation">.</span>childNodes<span class="token punctuation">,</span> <span class="token parameter">child</span> <span class="token operator">=></span><span class="token punctuation">&#123;</span>
            <span class="token keyword">if</span><span class="token punctuation">(</span><span class="token operator">!</span>child<span class="token punctuation">.</span>firstElementChild <span class="token operator">&amp;&amp;</span> <span class="token regex"><span class="token regex-delimiter">/</span><span class="token regex-source language-regex">\&#123;\&#123;(.*)\&#125;\&#125;</span><span class="token regex-delimiter">/</span></span><span class="token punctuation">.</span><span class="token function">test</span><span class="token punctuation">(</span>child<span class="token punctuation">.</span>innerHTML<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">&#123;</span>
                <span class="token keyword">let</span> key <span class="token operator">=</span> RegExp<span class="token punctuation">.</span>$<span class="token number">1.</span><span class="token function">trim</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
                child<span class="token punctuation">.</span>innerHTML <span class="token operator">=</span> child<span class="token punctuation">.</span>innerHTML<span class="token punctuation">.</span><span class="token function">replace</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">RegExp</span><span class="token punctuation">(</span><span class="token string">'\\&#123;\\&#123;\\s*'</span><span class="token operator">+</span> key <span class="token operator">+</span><span class="token string">'\\s*\\&#125;\\&#125;'</span><span class="token punctuation">,</span> <span class="token string">'gm'</span><span class="token punctuation">)</span><span class="token punctuation">,</span><span class="token keyword">this</span><span class="token punctuation">.</span>opt<span class="token punctuation">.</span>data<span class="token punctuation">[</span>key<span class="token punctuation">]</span><span class="token punctuation">)</span> 
                Observer<span class="token punctuation">.</span>target <span class="token operator">=</span> child
                <span class="token keyword">this</span><span class="token punctuation">.</span>opt<span class="token punctuation">.</span>data<span class="token punctuation">[</span>key<span class="token punctuation">]</span> 
                Observer<span class="token punctuation">.</span>target <span class="token operator">=</span> <span class="token keyword">null</span>
            <span class="token punctuation">&#125;</span>
            <span class="token keyword">else</span> <span class="token keyword">if</span> <span class="token punctuation">(</span>child<span class="token punctuation">.</span>firstElementChild<span class="token punctuation">)</span> 
            <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">compile</span><span class="token punctuation">(</span>child<span class="token punctuation">)</span>
        <span class="token punctuation">&#125;</span><span class="token punctuation">)</span>
    <span class="token punctuation">&#125;</span>    
<span class="token punctuation">&#125;</span>
<span class="token comment">// 常规观察者类</span>
<span class="token keyword">class</span> <span class="token class-name">Observer</span><span class="token punctuation">&#123;</span>
    <span class="token function">constructor</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">&#123;</span>
        <span class="token keyword">this</span><span class="token punctuation">.</span>subNode <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token punctuation">]</span>    
    <span class="token punctuation">&#125;</span>
    <span class="token function">addSubNode</span><span class="token punctuation">(</span><span class="token parameter">node</span><span class="token punctuation">)</span><span class="token punctuation">&#123;</span>
        <span class="token keyword">this</span><span class="token punctuation">.</span>subNode<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span>node<span class="token punctuation">)</span>
    <span class="token punctuation">&#125;</span>
    <span class="token function">update</span><span class="token punctuation">(</span><span class="token parameter">newVal</span><span class="token punctuation">)</span><span class="token punctuation">&#123;</span>
        <span class="token keyword">this</span><span class="token punctuation">.</span>subNode<span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token parameter">node</span><span class="token operator">=></span><span class="token punctuation">&#123;</span>
            node<span class="token punctuation">.</span>innerHTML <span class="token operator">=</span> newVal
        <span class="token punctuation">&#125;</span><span class="token punctuation">)</span>
    <span class="token punctuation">&#125;</span>
<span class="token punctuation">&#125;</span>
<span class="token operator">&lt;</span><span class="token operator">/</span>script<span class="token operator">></span>
<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<h2 id="参考链接"><a href="#参考链接" class="headerlink" title="参考链接"></a>参考链接</h2><p><a target="_blank" rel="noopener" href="https://juejin.cn/post/6844903619808985095">50行代码的MVVM，感受闭包的艺术</a></p>

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